Coextruded films having a layer of vinylidene chloride heteropolymers (PVDC) are used as barrier films to prevent passage of gasses, particularly as oxygen and water vapor barrier films in food packaging. Such barrier films may be about 2 mils thick and may further include layers of polyolefins. In such films, the barrier property is imparted by the PVDC layer. In some applications, it is useful to have an indicator uniformly distributed in the PVDC layer. In many plastics, indicators which may be detected by spectroscopy, are added via melt compounding. Such method of adding indicators is not useful for vinylidene chloride-based heteropolymers because the melt mixing step causes undesirable degradation, yellowing and black speck formation within the heteropolymer. Furthermore, the melt mixing step is costly. Indicators may be added to vinylidene chloride based heteropolymers by dry blending. However, when added in this manner, the indicator will not be evenly distributed throughout the heteropolymer and is further prone to segregation. Finally, dry blending step is also costly. Therefore, a cost effective method to uniformly distribute an indicator in PVDC would be desirable.